(mə-rān') A mass of till (boulders, pebbles, sand, and mud) deposited by a glacier, often in the form of a long ridge. Moraines typically form because of the plowing effect of a moving glacier, which causes it to pick up rock fragments and sediments as it moves, and because of the periodic melting of the ice, which causes the glacier to deposit these materials during warmer intervals. ◇ A moraine deposited in front of a glacier is a terminal moraine. ◇ A moraine deposited along the side of a glacier is a lateral moraine. ◇ A moraine deposited down the middle of a glacier is a medial moraine. Medial moraines are actually the combined lateral moraines of two glaciers that have merged.